(723b) Computational Design of MOF Arrays for Gas Sensing: Influence of Array Size on Sensor Performance

Authors: 
Gustafson, J., University of Pittsburgh
Wilmer, C. E., University of Pittsburgh

Gas sensors are used in applications ranging from assessing the quality of food products to  environmental monitoring.1 Existing sensors typically measure gas composition by indirectly detecting a change of mass or electrical resistance in a polymer or metal oxide substrate upon exposure to a gas mixture. When put in arrays, these gas sensing devices are called “electronic noses” and have improved capability in distinguishing varied gas mixtures. However, both polymer and metal oxide substrates typically have small surface areas, and so the concentration of adsorbed gases is low, which in turn leads to poor gas detection limits. Hence, the record high surface areas, reproducibility, tunability, and overall chemistry of MOFs make them ideal candidates as substrates for improved gas sensors. Furthermore, arrays of MOFs can significantly improve sensing capabilities over individual MOF sensors, but so far this strategy has not been systematically investigated. In this work, we show that a wide range of CO2, N2, O2, and CHgas mixtures can be distinguished by combining sensing input from arrays of MOFs of different types. Importantly, we show that although sensing performance is incrementally improved by using multiple similar (or identical) MOFs, dramatic improvements can be achieved by combining MOFs with different structural properties. We assume only a mass based response for each individual sensor, modeled after typical quartz crystal microbalance (QCM) devices, for which we assumed a 5 ng measurement error per sensor. Our findings are that using multiple types of MOFs can significantly reduce the size of the array needed to achieve the same sensing performance as an array of identical MOFs. We analyze the relationship between each MOF combination and how it distinguishes between gas compositions to determine the most optimal array for any given mixture. Finally, we briefly discuss plans towards an experimental implementation of our sensor design.

1. K. Arshak, E. Moore, G.M. Lyons, J. Harris & S. Clifford. A review of gas sensors employed in electronic nose applications. Sens. Rev. 24, 181–198 (2004).